



v\l / 



Fig. 8-8. Top, a pair of objective lenses, to 

 show the angle through which a lens can 

 gather light. Here a is the half-angle. Angu- 

 lar aperture = 2a. Bottom, a "zoom" micro- 

 scope. Courtesy Bausch and Lomb, Inc., 

 Rochester, New York. 



variable magnification and can be adjusted to provide the most con- 

 venience in viewing. 



By building a microscope with a very long body tube, any measure of 

 magnification could be achieved. Given a bright light source, a very large 

 image of a bacterial cell could be cast upon the moon. But magnification 

 alone is not the most important quality in microscopy. The ability to 



94 



